Logic input circuit with energy transfer with input voltage matching

ABSTRACT

A logic input circuit for an industrial equipment automatic control system supplied by a DC voltage source, in particular a battery ( 16 ), comprises a voltage step-up energy converter ( 12 ) composed of an inductance coil (L) and a switching transistor (TR), connected to the input (E 1 ) of the circuit ( 10 ); a logic level detector (DL) having a optocoupler; and a clock circuit (H) controlling the transistor (TR) by adjusting the frequency or the duty cycle to perform voltage matching with the signals applied to the input (E 1 ), and also the value of the voltage surge generated in logic high state ( 1 ) by the inductance coil (L) when switching of the transistor (TR) to the off state takes place.

BACKGROUND OF THE INVENTION

The invention relates to a logic input circuit for an industrialequipment automatic control system supplied by a DC voltage source, inparticular a battery, said input circuit comprising means for detectiondesigned to deliver a measurement signal representative of the logicstate when opening and closing of an input contact take place, with avery low heat dissipation.

STATE OF THE ART

A logic input board in electronic equipment for automatic controlsystems of in-board installations, in particular of rail transportvehicles, generally requires a large input current of about 10 mA. Theproblem arising in conventional equipment is then that of heatdissipation in the measuring resistors, as a logic input in a voltage of110 Volts for example, and a current with an intensity of 10 mA, willdissipate a thermal power of 1.1 W. The global heat dissipation isnaturally proportional to the number of logic inputs and often requiresthe use of cooling devices by heat sink or heat pipes to remove the heatto the outside. As electrical power supply of the equipment is performedfrom a safety power system with a battery bank, this results in additionin a loss of electrical power of the vehicle.

OBJECT OF THE INVENTION

The object of the invention is to achieve a logic input circuit for anautomatic control system, with voltage matching over a wide range ofinput voltages, and presenting a very low heat dissipation.

The input circuit according to the invention is characterized in that itcomprises:

a voltage step-up energy converter composed of an inductance coil and aswitching transistor, connected to the input of the circuit,

a logic level detector connected either between the inductance coil anda rectifier diode of an energy recovery circuit or between a chargingresistor and the DC voltage source,

and a clock circuit controlling switching of the transistor byadjustment of the frequency and duty cycle to perform voltage matchingwith the signals applied to the input, and also the value of the voltagesurge generated in logic high state by the inductance coil whenswitching of the transistor to the off state takes place.

Detection of the logic state is performed with a very low heatdissipation avoiding the use of heat sinks. Most of the energy isrestored to the battery by the energy recovery circuit. The presence ofthe energy converter associated to the inductance coil avoids voltagestep-up transformers having to be used.

The logic level detector advantageously comprises an optocoupler havingan emitting diode through which the measuring current flows, and areceiver delivering an image of the measurement signal to an acquisitioncircuit.

According to one feature of the invention, the energy recovery circuitis provided with a charging resistor connected in series between therectifier diode and the battery, or the emitting diode of the logiclevel detector. A first filtering capacitor is connected in parallelbetween the input potential reference and the mid-point of connection ofthe rectifier diode to the resistor. A second filtering capacitor isconnected between the two input terminals.

Other advantages and features will become more clearly apparent from thefollowing description of an embodiment of the invention given as anon-restrictive example only and represented in the accompanyingdrawings in which:

FIG. 1 represents the wiring diagram of a logic input circuit accordingto the invention;

FIG. 2 shows the wiring diagram of an alternative embodiment.

DESCRIPTION OF A PREFERRED EMBODIMENT

In FIG. 1, a logic input circuit 10 of electronic equipment for anindustrial automatic control system comprises an input E1 connected to avoltage step-up energy converter 12 comprising an inductance coil Lassociated to a switching transistor TR. The emitter of the switchingtransistor TR is connected to the input potential reference 13, and thecollector is connected to the mid-point 14 of connection of theinductance coil L to a logic level detector DL. The base of thetransistor TR is controlled by a dock circuit H designed to performvoltage matching of the input signals by adjusting the frequency andduty cycle. It is thus possible to apply voltage values comprisedbetween 24V and 110V to the input E1 depending on the type of battery16. The input potential reference 13 is at the potential of the negativepole of the battery 16.

The logic level detector DL is formed for example by an optocouplingelement 20 the receiver 20 b whereof delivers a measurement signal SE toa data acquisition circuit 22, said control signal SE beingrepresentative of the logic state on the input E1. The anode of theemitting diode 20 a of the optocoupler 20 is connected to the mid-point14, whereas the cathode is connected to the positive pole of the battery16 via a rectifier diode D1 in series with a resistor R. A firstfiltering capacitor C1 is connected in parallel between the inputpotential reference 13, and the mid-point 24 of connection of the diodeD1 to the resistor R. A second filtering capacitor C2 is connectedbetween the input potential reference 13 and the other input E1.

The rectifier diode D1, resistor R and first filtering capacitor C1constitute an energy recovery circuit 26, the outputs S1 and S2 whereofare connected in parallel to the terminals of the battery 16.

The switching transistor TR can be formed by a MOS, FET, IGBT, etc.transistor. The other logic input circuits (not represented) areidentical to the one described previously and are all connected inparallel to the terminals of the battery 16.

Operation of the logic input circuit 10 is as follows:

The elements of the logic input circuit 10, in particular the switchingtransistor TR, are dimensioned for the maximum input voltage, forexample 110V. The input E1 can be voltage matched by adjusting thefrequency of the dock circuit H and by adjusting the duty cycle thereof.It thus enables the time during which the switching transistor TR isturned on and off to be adjusted.

In logic low state (0), the voltage applied to the input E1 is zero andturn-off of the diode D1 prevents any current flow in the inductancecoil L, whether the transistor TR is on or off. The optocoupler 20 alsoremains off and there is no current flowing therethrough.

In logic high state (1), the voltage applied to the input E1 isappreciably equal to the voltage of the battery 16. When the transistorTR is turned on, a current is established between the input E1 and theinput potential reference 13 flowing in the inductance coil L. After thetransistor TR has switched to the off state, the inductance coil Lgenerates a voltage surge at the terminals of the transistor TR and thepotential of the mid-point 14 becomes higher than that of the output S1connected to the positive pole of the battery 16. A mean current ofabout 10 mA is then established in the direction of the battery 16,passing through the resistor R. Detection of the logic high state (1) isperformed by transmission of the measurement signal SE to theacquisition circuit 22, which transmission is performed with a very lowheat dissipation, since most of the energy is restored to the battery 16by the energy recovery circuit 26.

The voltage increase at the mid-point 14 is relatively low to preserve agood efficiency, but sufficient to ensure flow of the mean current of 10mA. The value of the voltage increase is a function of the duty cycle ofthe transistor TR, and enables the logic input circuit 10 to work inconstant current regardless of the input voltage. The terminal of thetransistor TR opposite the mid-point 14 is advantageously at the inputpotential reference, which simplifies simultaneous control of severaltransistors in case of a plurality of logic inputs in parallel.

With reference to FIG. 2, the optocoupler 20 is removed from the frontend to the DC side being electrically connected between the resistor Rand the DC voltage source 16.

What is claimed is:
 1. A logic input circuit for an industrial equipmentautomatic control system supplied by a DC voltage source, in particulara battery, said input circuit comprising means for detection designed todeliver a measurement signal representative of logic low state and oflogic high state, comprising: a voltage step-up energy convertercomposed of an inductance coil and a switching transistor, connected tothe input of the circuit, a logic level detector connected eitherbetween the inductance coil and a rectifier diode of an energy recoverycircuit or between a charging resistor and the positive pole of the DCvoltage source, and a dock circuit controlling switching of thetransistor by adjustment of the frequency and duty cycle to performvoltage matching with the signals applied to the input, and also thevalue of the voltage surge generated in logic high state by theinductance coil when switching of the transistor to the off state takesplace.
 2. The logic input circuit according to claim 1, wherein theswitching transistor is connected between the input potential referenceand a mid-point of connection of the inductance coil to the logic leveldetector or to the rectifier diode.
 3. The logic input circuit accordingto claim 1, wherein the logic level detector comprises an optocouplerhaving an emitting diode connected between the inductance coil and therectifier diode, and a receiver delivering said measurement signal to anacquisition circuit.
 4. The logic input circuit according to claim 1,wherein the logic level detector comprises an optocoupler having anemitting diode connected between the charging resistor and the positivepole of the voltage source, and a receiver delivering said measurementsignal to an acquisition circuit.
 5. The logic input circuit accordingto claim 1, wherein the resistor of the energy recovery circuit iselectrically connected in series between the rectifier diode and thebattery or the emitting diode.
 6. The logic input circuit according toclaim 5, wherein a first filtering capacitor is connected in parallelbetween the input potential reference and the mid-point of connection ofthe rectifier diode to the resistor.
 7. The logic input circuitaccording to claim 6, wherein a second filtering capacitor is connectedin parallel between the input potential reference and the input.